Motor-driven chain saws and other hand-held portable tools of this kind must always be capable of functioning even in extreme weather conditions, for instance, at -30.degree. C. during the winter and at +30.degree. C. in the summer. If the motor-driven chain saw is used in winter, it is known for the cooling air, heated at the engine cylinder, to be supplied to the carburetor as preheated intake air. The preheated intake air may be supplied either via a blower or, lacking a blower, merely by a suitable flow brought about by underpressure or overpressure. In summer operation, the pass-through opening for the heated cooling air leading to the carburetor must be closed. To this end, it is known to provide removable inserts with which the overflow openings in the housing can be covered.
Another arrangement is also known, in which the pass-through opening for the warm air that is to be supplied to the carburetor can be opened or closed selectively by a pivotally mounted flap. This hinged flap, which is pivotable about an axis, is substantially flat and merely effects opening or closure of the pass-through opening. Thus, when the hinged flap is open, only a relatively small portion of the total amount of heated cooling air flowing around the cylinder is delivered to the carburetor, while the remaining majority of the heated cooling air is vented directly into the open, as during summer operation. This has the substantial disadvantage that in winter operation, especially at extremely low outdoor temperatures and thus when the intake air is very cold, the heating of the carburetor is inadequate because the carburetor is supplied with too little preheated air. Inadequate heating of the carburetor during winter operation causes icing of the carburetor, or icing of the intake filter of the motor-driven chain saw depending on the weather conditions and on the possibility of snow entering the same, and so a malfunction-free operation is not assured.